The top U.N. official investigating North Korean human rights abuses is urging South Korea not to undermine international efforts to prosecute the Kim Jong Un regime.

Seoul is trying to reduce border tensions and continue its long-term strategy to achieve the peaceful reunification of the Korean peninsula, but the U.N. special rapporteur on human rights in North Korea said the South’s policy should not ease international pressure against the North.

“While unification is paramount, accountability measures for crimes against humanity need to be laid down firmly and robustly by the international community,” said Marzuki Darusman the Untied Nations Special Rapporteur on the human rights situation in North Korea.

Darusman is part of the U.N. Commission of Inquiry that documented a network of political prisons in North Korea and atrocities that include murder, enslavement, torture, rape, and forced abortions.

Its report led to a U.N. recommendation to refer North Korea to the International Criminal Court for crimes against humanity. The General Assembly endorsed the recommendation last year but the measure has since been stalled in the Security Council, where China and Russia hold veto power.

North Korea denies allegations

North Korea has denied committing the alleged abuses, but has refused to allow independent inspectors into the country to investigate.

The U.N. Special Rapporteur was in Seoul this week to visit a new Office of High Commissioner for Human Rights that was established in the South Korean capital to monitor and investigate ongoing claims of abuse in North Korea.

As tensions raised to the point of a near military clash between the two Koreas in August, Seoul and Pyongyang have agreed to resume reunions of families separated by the Korean War that ended in 1953 and to pursue further dialogue and exchanges.

Korea analyst Go Myong-Hyun at the Asan Institute for Policy Studies in Seoul said Darusman’s comments were aimed not at the conservative government of President Park Geun-hye, which supports sanctions and deterrence against the North, but at opposition groups that believe the international community should limit its role to pursuing nuclear disarmament on the Korean peninsula.

“I think there are some segments of South Korean society that thinks that the human rights issue in North Korea is not really an international issue but an inter-Korean issue,” said Go Myong-Hyun.

US’ Cuba policy a factor

These groups cite the Obama administration’s recent moves restoring relations with Cuba, saying increasing engagement and trade ties will help improve relations and offer the North incentives to open its society.

Darusman admits that prosecuting Kim Jong Un and other key North Korean leaders for crimes against humanity complicates efforts to search for a political resolution to the ongoing separation of the two Koreas.

“Now I see of course the, I wouldn’t say contradiction, but let us say the distinction between an accountability process and a unification exercise,” said Darusman.

But Go Myong-Hyun said the U.N’s pursuit of North Korean human rights abuses is in a way an acknowledgement that the international community does not believe Pyongyang is willing to engage in meaningful talks to end its nuclear weapons program.

“North Korea took the nuclear issue off the table anyways, [so] then there is no downside to press on the human rights issue,” said Go Myong-Hyun.

North Korea’s provocative rhetoric and actions also work to undermine any attempts to increase engagement with the South.

In August tensions between the two countries escalated to the brink of war after landmines planted by Pyongyang on the South’s side of the border area’s demilitarized zone (DMZ) detonated and injured two soldiers.

There are also reports that North Korea is preparing to launch a long-range missile, possibly as soon as next month to mark the 70th anniversary of the founding of the ruling Workers’ Party.